The invention relates to a fibre-reinforced composite ceramic containing high-temperature-resistant fibres based on Si/C/B/N which are reaction-bonded to a matrix based on Si.
Such a process and such a composite ceramic are known from DE-A-4 438 455.
Carbon fibre-reinforced carbon (C--C, also known as CFRC or in German language usage as CFC) is among the composite ceramic materials which have been introduced successfully some time ago.
Recently developed high-performance brake systems based on CFRC brake discs with specially developed friction linings, as are used, for instance, in car racing, can, however, only be produced using numerous impregnation or carbonization and graphitization cycles, so that the production process is an extremely time-consuming, energy-intensive and costly process which may take a number of weeks or months. Furthermore, CFRC brake discs for use in production vehicles operated under normal conditions have totally unsatisfactory braking properties in the presence of moisture and when operated at low temperatures. This shows up, inter alia, in decidedly non-constant coefficients of friction as a function of the operating temperature and the surface lining which makes regulation, as hitherto customary in 4-channel ABS systems, extraordinarily difficult or even impossible. In view of this background, attempts are being made to develop improved fibre-reinforced composite ceramic materials which, for example, can be used as brake discs for high-performance brake systems in motor vehicles or railway vehicles. In addition, such fibre-reinforced composite ceramic materials are also of interest for numerous other applications, for instance as turbine materials or as materials for sliding bearings.
Although silicon-infiltrated reaction-bonded silicon carbide (SiSiC) containing from 2 to 15% by mass of free silicon has been known since the 1960s and has also been introduced commercially for some applications in the field of heat engineering, the production of SiSiC materials is also very complicated and expensive.
The abovementioned DE-A-4 438 455 discloses a process for producing a fibre-reinforced C-SiC composite ceramic in which the green body is made up of resin-impregnated fabrics. A disadvantage of this process is that the building-up or production of complicated structures from such precursors, which themselves are not exactly cheap, is very cumbersome and results in a great deal of scrap. The known process is therefore not suitable for use in mass production of components such as brake discs. The laminated structure additionally leads to strong anisotropy of various properties of the body produced in this way, which has an adverse effect on, in particular, heat removal from the brake disc. Furthermore, such brake discs have a tendency to delaminate under some conditions as they wear, which is particularly dangerous.